The present invention relates to an improved press and safety latch means therefor. One aspect of the invention is to provide safety latch means of high load carrying ability as fail-safe means in a press mechanism to guard against failure of power such as derived from hydraulic, electrical, or pneumatic sources or the like. An aspect is to provide an improved press having one or more safety latches such as this incorporated therein. The invention will now be described with reference to a press or clamp of the sort generally described in my above noted pending application, that is, one adaptable for use in liquid reaction molding and having a C-shaped frame assembly that is swingable with reference to a pedestal and base plate assembly, the C-shaped assembly, in turn, having a crown or upper mold support pivotally mounted in the upper jaw of the C-shaped frame.
A clamp or press of the type here described has hydraulic piston and cylinder combinations for use as its power means whereby to turn the C-shaped frame relative to the pedestal and whereby to turn the crown or upper mold support platen in a pivotal manner relative to the C-shaped frame. Loss of hydraulic pressure, failure of electrical utilities which may be pumping the hydraulic liquid up to the needed pressure, or failure of other utilities such as compressed air or the like may cause the moving parts of a press such as this to stop operation. Further, in the absence of restraining means, the press parts may return rapidly to a home position. Where the return to home is unintentional such as caused by power loss or the like, a safety hazard exists. The very mass of such clamp or press parts is so great that a mechanically positive safety latch means is deemed necessary to protect the operator or other persons who may be in the vicinity.
A fail-safe device against power failure on a clamp or press of the nature contemplated has severe service conditions which it must meet. For example, the present system has been applied to a 75 ton clamping force press (clamp) where a mold half may weight about 7 and 1/2 tons and be moved with its center of gravity about a radius of 1.5 - 2.7 feet. This is an enormous torque which must be controlled to provide maximum safety. As another example, the C-shaped frame member (further described in my co-pending application and below) may weigh about 15 tons and have mold halves weighing approximately 15 tons, totalling a 30 ton weight being swung about a radius of 1-1.5 feet which also requires control of this large torque in a positive fashion. Such control would -- and herein does -- arrest the return to home position under natural forces, e.g. gravity.
A safety latch comprising a mechanical brake is a possible solution to this, but the very large torques would require an enormous brake and would be susceptible to some slippage derived from dirt and other deposits settling on the braking surfaces. Also, a mechanical brake relies on friction rather than a mechanical block.
Another prior art stopping means consist in a shot pin or detent device. Such devices have a number of defects such as requiring moving the shot pin in and out of a hole every time the mechanism brings the pin and hole into conjunction which requires additional mechanism and inherently provides a lot of wear on the fail-safe devices.
A traditional ratchet and pawl device is not satisfactory here either because of the line contact between the pawl and the ratchet tooth or tooth space which it engages. My invention, among other things, aligns the pawl with the ratchet tooth space so that area contact is achieved. Also, the tremendous tonnages are successfully coped with by providing the pawl with a unique type of journal bearing. And finally, the present invention needs small unlatching power and mirror backing off when reversing the direction of movement.
Thus, the invention has among its objectives, advantages, and/or features providing an improved ratchet and pawl machine used as a safety latch, i.e., as a fail-safe device, to prevent one part of a press or like mechanism from accidentally swinging to a home position (for example under the force of gravity) about a first axis and relative to another part, which machine includes -- a ratchet that is adapted to be secured in a fixed relationship to or upon the one part and having a plurality of equally spaced teeth arranged along an arc coaxial with the first axis; a pawl supported to pivot about a second axis and which is mainly peripherally defined by an arcuate bearing surface coaxial with the second axis, a pawl tooth connected to one end of said bearing surface, and a neutral surface connecting the other end of said tooth with the other end of said bearing surface, the tip of the tooth being at a radius from the second axis less than the radius of the arcuate bearing surface; and a pawl bearing for said pawl and which is fixedly secured to the other part mentioned above and has an arcuate concave bearing surface so shaped and sized as to revolvably receive and support the pawl arcuate bearing surface therein. The pawl bearing actually receives and revolvably supports the pawl by means of the latter's arcuate bearing surface. It is important that the sum of the ratchet tooth radius and the pawl tooth tip radius are greater than the distance between the first and second axes. A means is provided to bias the pawl tooth into engagement with a space between the ratchet teeth -- preferably a helical spring under tension is provided for this purpose.
This invention also comprehends the combination of a clamp or press with one or more such ratchet and pawl machines. In the preferred embodiment, such a combination comprises a C-shaped frame assembly that is supported by a pair of journals (trunions) to swing relative to a fixed base or support (called a pedestal assembly) and on which is mounted a pair of mold supports, the upper one of which (called a crown) is swingable with reference to the C-shaped frame. The home position contemplates that the column part of the frame be substantially vertical and the jaws thereof substantially horizontal. To this combination, the present invention brings a safety latch mechanism comprising a ratchet secured to the crown to swing therewith and a pawl secured to the C-shaped frame whereby to latch the crown relative to the frame when called upon, and further includes a similar ratchet and pawl system for latching the C-shaped frame relative to the fixed base and having the ratchet on the frame supported to swing about the trunion or journal bearings thereof and a pawl mounted on the pedestal assembly to engage the same in a safety latching manner whereby both the swinging C-shaped frame and the swinging platen or crown may be latched in place in the event of a power failure.
An object of this invention is to provide an improved fail-safe machine for incorporation in other mechanisms. An object of the invention is to provide an improved combination of a fail-safe device with a mechanism of the sort described in my co-pending application. Still another object of the invention is to provide an improved mechanism of the type described in my co-pending application having a plurality of these fail-safe devices placed thereon to control displacement of the elements should power failure occur.